Trucks have long been used to transport cargo of various weights and dimensions. In order to be transported, the cargo must first be loaded onto the truck bed and then off-loaded upon arrival at the cargo destination. Handling heavy cargo or cargo with unusual dimensions is often problematic due to the loading and unloading difficulties that are presented with such loads. There are various types of trucks commercially available, but all have a fixed cargo bed design and, therefore, require special equipment or techniques for loading and unloading cargo onto the bed.
To load cargo onto a fixed-bed truck, it is typical to employ a temporary ramp that is rigged with one end of the ramp resting against the tailgate of the truck and the other end of the ramp resting on the ground. The cargo must then be pushed, pulled, or rolled up or down the ramp as the case may be to place the cargo on the bed of the truck or to move it off of the truck bed. Another way to load cargo onto a truck bed is to back up to a platform that is at about the same elevation as the truck bed and then push, pull, slide or roll the cargo on or off the truck bed. Still another way to load cargo onto, or off of, a truck bed is to use equipment designed to lift and move heavy loads, such as a dolly, chain fall, or lift truck.
While each of the aforementioned means can be used to move cargo onto or off of a truck bed, each has its limitations and drawbacks. Ramps, for example, are typically temporary devices that require space behind the vehicle. The ramps may slip off of the truck bed or tailgate and, unless the ramps are unusually long, present a steep angle that must be overcome in moving the cargo up the ramp. If the cargo to be loaded is at a residence or in the middle of a forest, for example, there is usually no platform at the same elevation as the truck bed to back up to in order to load or unload the cargo. Special equipment may not always be available and, if available, may be difficult, if not impossible, to use in certain conditions or locations.
Pivoting truck beds and vertically-adjustable tailgates were introduced as having advantages that overcome the drawbacks and limitations of a fixed truck bed arrangement. Pivoting beds include a bed pivotally connected to a chassis above the rear axle. The front of the bed is releasably connected to the vehicle to maintain the bed in a substantially horizontal orientation. Cargo loading is accomplished by releasing the front of the bed allowing the bed to pivot until the rear of the bed contacts the surface on which the vehicle is positioned. The bed then forms a ramp onto which the cargo may be rolled, pulled or pushed.
Vertically-adjustable tailgates are typically pneumatically operated such that the tailgate can be raised or lowered via pneumatic controls. While these vertically-adjustable tailgates can be found on cube vans and stake trucks, they are not usually found on pick-up trucks.
While eliminating some of the drawbacks and limitations of fixed truck beds, pivoting beds and vertically-adjustable tailgates have their own drawbacks and limitations. Even though pivoting beds reduce some loading problems, the heavy cargo must be pushed or pulled up the inclined bed which is then prone to unexpected movement when the center of gravity of the cargo moves past the pivot point of the bed. Vertically adjustable tailgates are limited in the size and weight of cargo they can handle and may require counter-balancing if the load is extremely heavy.
In still another attempt to eliminate these drawbacks and limitations, there has been shown an adjustable bed pivotally disposed in a U-shaped frame of a vehicle wherein boomerang linkages allow the bed to move vertically up and down while maintaining a substantially horizontal orientation. In yet another attempt, a vehicle is provided with an elevatable cargo box in a U-shaped cargo area wherein the cargo box is movable between elevated and lowered positions by cables. However, these attempts require an elaborate linkage system to facilitate movement of the bed beyond the frame of the vehicle in the one case, and an elaborate cable system in the other case.
Another common disadvantage with all vertically moveable truck beds is the lack of stability and support in the cargo-carrying section of the truck. The typical U-shaped frame in all vehicles with vertically-moveable beds does not have the structural rigidity and support necessary to provide a horizontally stable bed while the vehicle is in motion.
From the foregoing, it would be desirable to have a truck with a bed capable of being raised and lowered for ease in loading and unloading of cargo. It would also be desirable to have a truck with a vertically adjustable bed that has more frame stability and structural support to provide a horizontally stable bed while the vehicle is in motion.